Ayres's Description of a New Genus of Fishes. 59 
of the bone extends about half an inch, overlapping the max- 
Mlary, outside of which it terminates by a thin edge. On 
this bone are the two or three larger anterior teeth of the 
upper jaw. ‘The two bones are so united as to allow of very 
little separate motion. The maxillary begins by a thin edge, 
inside the intermaxillary, near the anterior extremity of the 
mouth, and passes backward the whole length of the jaw. 
The principal row of teeth, and the partial row exterior to 
them are on this bone. - On its posterior superior angle, we 
find the little supplementary bone which exists in so many 
fishes ; it is more than half au inch in length. "The maxillary 
reaches within about a tenth of an inch of the angle of the 
lower jaw. 
The lower jaw is straight, thin, and narrow. The angle 
formed by the two branches at their symphysis is very acute. 
In the structure of the jaw we meet with nothing worthy of 
note; but its articulation is most singular. The movable 
cheek of the fish, which covets the gills and makes the side 
of the mouth, is in form a very acute-angled triangle, nearly 
isosceles. One of the sides of this triangle is the upper jaw; ` 
the base is a line stretching from the front of the mouth 
obliquely upward and backward, across the eye to the upper 
angle of the gill-opening ; the third side is formed by a slen- 
der, nearly straight, apparently single bone, reaching from the 
upper angle of the gill-opening downward and backward to 
the apex of the triangle, where it affords attachment for the 
lower jaw. This appears like a perfect anomaly, that a single 
bone should form the connection between the lower jaw and 
the cranium. The anomalous structure, however, is in part 
explained by removing the integuments. The bone, though 
Single; shows traces of divisions, in such manner as to con- 
vince us that three distinct bones are united in its formation. 
One commencing at the articulation of the lower jaw, passes 
upward, along the posterior border, becoming: narrower as it 
ascends, Thisis the jugal. It terminates about half an inch 
' the cranium. In front of it is another, which must be 
